Have you tried adding the dialog line in advancedsettings.xml? This solved the stuttering problem when opening the osd or when backward.
<gui>
<algorithmdirtyregions>0</algorithmdirtyregions>
</gui>
If you have CE NE 22 (I consider the 20241210 best version for s905x4) the most correct solution that worked best was
<gui>
<algorithmdirtyregions>0</algorithmdirtyregions>
<fronttobackrendering>true</fronttobackrendering>
<geometryclear>false</geometryclear>
</gui>
Apparently, the last nightly CE NE 21.2 20250412 fixed this stuttering problem, without needing to change anything in advancedsettings.xml, but anyone who watches something with subtitles will experience micro stuttering when subtitles appear on the screen.
I tested CE NO 22, no stuttering, but I think the kernel is very bad for s905x4! Content in 4k high bitrate 80mbps+ is slow, problems with seek, etc.